Antarctic skill is one of the most available large-scale sources of substantial expansion of the output of protein food of animal origin. The catch of krill may well surpass the total currently attained level of the catch of fish in the World Ocean. The most valuable component of the krill is its pure meat in the form of muscular tissue lumps. The chemical composition of the krill meat is similar to that of the meat of crabs and shrimps and includes various vital amino-acids and microelements. To use the krill meat as food, it has to be completely separated from the shell. Pure meat extracted from the krill has to have the minimum content of lipids, the remnants of the liver and of the contents of the gastrointestinal tract, which last-mentioned components affect the quality of the meat and its storability.
When one considers the great distances where the krill is caught and the long time it takes to carry the krill to the consumers, it is obvious that the krill should be processed directly in the catching areas into pure meat either as a ready-to-use produce (natural canned krill), or as a semi-finished product (fresh-frozen krill meat).
There are known apparatus for removing the shell of crustaceans, including a belt conveyer for feeding the crustaceans, a helical passage wherein the crustaceans are advanced by rotating discs having on their periphery sharp spikes breaking up the shell and separating it from the meat. Then the meat and the shell fragments are finally separated by flotation.
Apparatus of this kind enables obtaining the meat of shrimps in lumps: however, they are operable solely for processing shrimps of a relatively large size and would not be practically suitable for removing the shell of small crustaceans, e.g. ocean shrimps.
There is also known an apparatus for automatic removal of the shell of crustaceans (e.g. shrimps), including a charging mechanism in the form of a longitudinal belt conveyer, slit-type devices for sorting the crustaceans into fractions according to their size, the narrowing guides of a trough for indexing the crustaceans one by one, and a device for removing the shell, including a shell breaking-up mechanism and a unit for removing the shell fragments, an air conduit and a compressed air supply pipe.
In the known apparatus the crustaceans sorted according to their size are indexed into a predetermined position and directed one by one in an air stream into the shell-breaking channel where the shell is stripped by blades and knocked-off by shell-removing elements, whereafter the stripped shrimps are separated from the shell with the use of a fan.
In the known apparatus of this type it is necessary to classify the shrimps according to their size and to feed them for processing one by one, which curbs down the throughput of the apparatus. With each fraction of the corresponding size being directed for the processing into its own bin adjoined by an oval-section tubular passage corresponding to the contour of shrimps of the respective size, the apparatus has a relatively complicated structure.
There is further known an apparatus (cf. the U.S. Pat. No. 3,408,686; Cl. 17-2, dated 1968) for separating the heads of shrimps from their bodies, comprising a mechanism for breaking up the shrimps and a mechanism for separating the decapitated bodies of the shrimps from their heads, the legs or pleopods and their components.
The shrimp breaking-up mechanism includes a charging funnel, a vertical duct with guides and a horizontal duct with a stationary sharp blade or rib, a gate regulating a high-velocity jet, a wire scraper, means for decelerated the high-velocity jet and a pump for feeding the working fluid.
The mechanism for separating the decapitated body from the head, legs or pleopods and other components includes a vertical cylindrical vessel and a chamber for feeding the mixture.
The vertical cylindrical vessel includes a perforated partition, a settling pipe running axially of the vessel, a conduit opening into the central portion of the settling pipe, a trough communicating with the upper portion of the settling pipe and an inclined conduit for removing the bodies, accommodated under the lower portion of the settling pipe. The mixture-feeding chamber is a tank communicating with the vertical cylindrical vessel via an inclined pipe and a transfer tray.
The apparatus operates, as follows.
Crustaceans are fed into the charging funnel of the shrimp breaking-up mechanism where they fall down the vertical duct, and the guides direct them to become positioned vertically on the stationary sharp blade arranged at the intersection of the vertical and horizontal ducts. The high-velocity jet or stream of the working fluid is driven by the pump through the horizontal duct where it forces either the head or the body of a shrimp against the sharp blade, whereby the head becomes separated from the body. Then the high-velocity stream carries the body of the shrimp past the wire scraper which tears the legs or pleopods off the body. The high-velocity stream then carries out the mixture of the heads, bodies, legs or pleopods and other components of the shrimps from the shrimp breaking-up mechanism, and directs the mixture into the mechanism for separating the bodies from the rest of the components.
The process of separating the bodies from the other components is carried out, as follows.
The mixture in the stream of the working fluid gets into the mixture feeding chamber wherefrom it is guided along the inclined pipe and the transfer tray into the conduit communicating with the settling pipe of the vertical cylindrical vessel, the major portion of the working fluid flowing through the perforations of the transfer tray into the perforated paratition, to fill the vertical cylindrical vessel and to produce a uniform flow of the working fluid both within the vertical vessel and inside the settling pipe. The permament level of the working fluid in the vertical cylindrical vessel provides for a permanent flow rate or velocity within the settling pipe, in the inclined conduit for removing the bodies and in the trough. The separation of the bodies from the other components takes place within the settling pipe, owing to the upward flow of the working fluid having the sufficient viscosity for the ascending travel of the heads, legs or pleopods and other components, and the descending motion of the bodies. These decapitated bodies leave the settling pipe through its lower portion, get into the inclined conduit for removing the bodies and are carried away from the apparatus, whereas the rest of the components ascend along the settling pipe and are carried away through the trough.
The apparatus of the prior art is intended merely for decapitating the shrimps and enables separating their bodies, not the muscular tissue devoid of the shell, liver, gastrointestinal tract, and thus ready for use as food. The shell breaking-up mechanism is based on one by one decapitation, with the shrimps positively retained on the stationary sharp blade or rib, which reduces the throughput of the apparatus. The mixture-feeding chamber, the charging conduit, the settling pipe, the trough and the inclined body-removing conduit have to have maintained therein the constant rates or velocities of the flows of the working fluid, which complicates and opposes active control over the processes of the separation of the components. The self-sustained withdrawal of the working fluid separately carrying away the bodies and the rest of the components likewise complicates the continuous trouble-free performance of the apparatus.
Thus, the hitherto known apparatus for processing small crustaceans, solving as they do to different degrees the problem of yielding a product usable as food, offer limited capabilities of obtaining pure meat of small crustaceans. They would not enable introduction of an automated high-capacity process of treating the antarctic krill--the promising source of valuable food products.